Method and apparatus for the continuous countercurrent extraction of sugar from bagasse

ABSTRACT

Method and apparatus for the continuous countercurrent extraction of sugar from bagasse or comminuted sugar cane. In extracting sugar from bagasse the bagasse is subject to the action of extraction liquid in a diffusion trough through which a layer of bagasse is passed by conveyor means, the bagasse being supported on a screen in the bottom of the trough and through which the extraction liquid percolates and is collected in containers beneath the trough, the extraction liquor in the trough being recirculated. The method of this invention consists in subjecting the layer of bagasse to pressure such as by means of a roller prior to discharge of the bagasse from the trough in order to extract liquid therefrom, movement of the bagasse, when undergoing liquid extraction, being retarded while the rate of travel of the conveyor means remains constant. In apparatus for carrying out the invention a roller is positioned in the discharge end of the trough for maintaining pressure on the layer of bagasse, the rate of rotation of the roller being controlled by a suitable braking device.

ELECTROGRAPHIC PRINTING ELEMENT This invention relates to electrographic printing, and more particularly to an improved coated product useful in making printed copies, as well as a unique electrographic printing process whereby prints are produceable from the coated product.

Electrographic printing, as the term is used herein, refers to an electrostatic printing process which differs from and is not to be confused with another form of electrostatic printing process often referred to as electrophotographic printing. in an electrographic printing process, an image-defining electrostatic charge is laid directly down upon an insulating or dielectric surface, using such electronic devices as a cathode ray tube, a pin matrix and pulsing corona discharge, or by means of a direct image transfer from one surface to another. In comparison, in the electrophotographic printing process a copy sheet including a photoconductive layer may first be given a uniform charge over its entire surface in the dark. Then, an image-defining charge pattern may be formed by exposure of the charged photoconductive layer to light through a positive image, much like a photographic process.

The two types of processes differing as they do in the manner in which an image is formed, have distinct requirements with respect to the type of copy sheet or product best used in the process for the reproduction of an image. Prior art patents which discuss electrographic printing and problems related to this type of printing comprise US. Pat. Nos. 3,075,859 and 3,1 l0,62l.

Speaking in general terms, a product used in making electrographic prints, such as a copy sheet, should include means for presenting a dielectric or insulating surface for the reception of the image-defining electrostatic charge, most usually in the form of a thin film or layer of dielectric materiaLand support for this film which is electrically conductive, whereby any stray electrical charges'in the means supporting the film are dissipated to produce clearer prints. With a suitable dielectric material selected for the film, which is capable of accepting a charge transferred thereon and retaining this charge, best print resolution and density and minimum background result in a print produced from the copy sheet if the dielectric film is relatively thin, as this inhibits tendencies of the dielectric film to retain in the body thereof a diffused and scattered charge emanating from the sharply defined charge laid down on the surface of the film. With a conductive surface spaced relatively close to the charge receiving surface of the dielectric film, as is possible when the dielectric film is quite thin, any of such scattered charges are quickly dissipated through the conductive surface.

In general terms, an object of this invention is to provide a novel copy product, more specifically a copy sheet, for receiving an image defining electrostatic charge, that features a novel conductive backing for the dielectric or insulating film in the product.

More specifically, an object is to provide an improved copy product, ordinarily a copy sheet, including a dielectric or insulating film for receiving an image defining electrostatic charge, that further comprises a layer of material backing the dielectric film which possesses requisite electrical conductivity at the time that an image defining charge is deposited on the dielectric film, without depending upon the presence of humidity conditions within a limited range to obtain this conductivity. To further explain, with certain types of copy sheets including a dielectric film spread over a base paper sheet, conductivity in the base paper sheet is relied upon to provide the necessary conductive base for the dielectric film. This conductivity is largely the result of certain moisture conditions in the base paper sheet, and as a consequence, certain humidity conditions are necessary to obtain proper quality in copies produceable with the sheets. With the copy sheets of this invention, this dependence upon specific range of humidity conditions is largely eliminated.

Yet another object of the invention is to provide a novel method of producing a copy, in an electrographic printing process, wherein a copy sheet or product is excited by a pretreatment before depositing an image defining electrostatic charge on the dielectric film of the product, which excitement produces the desired conductivity in a layer of material backing up the dielectric film that receives the charge.

A related object is to provide such a process where the treatment to produce excitement comprises a light treatment of a photoconductive layer, which is easily and quickly done before depositing an image-defining electrostatic charge on the dielectric film.

In a specific embodiment of the invention, and also contemplated herein as an object, a paper base sheet is provided having over both faces thereof a layer of photoconductive material which is excited by light to become electrically conductive. Over the layer, on one side of the sheet only, there is provided a dielectric film which is translucent, i.e., light permeating and preferably nearly transparent, and which, therefore, enables the passage of light from a light source on said one side of the sheet through the film to excite and make conductive the photoconductive layer between the film and the paper base sheet. The photoconductive layer on the opposite side of the paper base sheet may also be excited by a light source on the opposite side of the sheet, and the two layers together form a backing for the dielectric film which will dissipate substantially completely any stray charges and produce with a relatively thin spread of dielectric material prints with high density, good resolution and a minimum of background.

As a feature related to the above, it is contemplated that in producing a copy from a copy sheet comprising a photoconductive layer over opposite faces of a paper base sheet, the photoconductive layers on opposite sides of the sheet will first be excited by exposing these to light sources disposed on either side of the sheet to prepare the copy sheet for the reception of an electrostatic image-defining charge.

These and other objects and advantages are attained by the invention and the same is described hereinbelow in conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view, somewhat enlarged, of portions of a copy sheet according to one form of the invention, and illustrating various layers making up the sheet; and

FIG. 2 is a similar cross-sectional view of a modified form of copy sheet as contemplated herein.

As indicated above, in an electrographic printing process an image-defining electrostatic charge is deposited on a dielectric or insulating film, and such charge is retained on the film whence it is utilized to develop a printed image as by dusting the surface of the film with a powder, toner or colored resinous substance in particle form, with such substance having an opposite electrostatic charge to the charge deposited on the dielectric film. To produce best line definition and image resolution, the dielectric film should extend over a conductive layer, and in most applications it has been noted that a conductivity level within the range of about 10 to 10 ohms/square surface resistivity is desirable. While a copy product comprising a metal sheet forming the backing for the dielectric film is possible, as a practical matter and to produce copy sheets of low-cost and in high-volume, a paper base sheet is employed.

With a paper base sheet, or other sheet or web of cellulosic material, the requisite conductivity in the sheet may exist if the sheet has a certain moisture content. However, such a product depends upon relative humidity conditions for good resolution and detail to be obtained in a reproduction. To eliminate this dependence upon relative humidity conditions, and to enable the uniform production of good copies, the copy sheet of this invention features a layer of material under the dielectric film which is excited before an electrostatic image is deposited on the copy sheet by a pretreatment which renders the layer suitably conductive regardless of specific humidity conditions. Thus, and according to this invention, a copy sheet is prepared by coating paper on at least one side with a coating of photoconductive material, which extends as a substantially continuous layer over this one side. A coating is then applied PNENIEBEEZIHH 3.629.001

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SHEET 5 OF 6 PATENTEB DEBZI lsn SHEET 8 [1F 6 METHOD AND APPARATUS FOR THE CONTINUOUS COUNTERCURRENT EXTRACTION OF SUGAR FROM BAGASSE The invention relates to a method and apparatus for the continuous extraction of sugar from sugar cane and is an improvement in or modification of the invention, disclosed in US. Pat. No. 3,501,345 to W. Kaether and W. Dietzel.

The invention comprises a method for the preliminary extraction of water and extraction of sugar from bagasse which is continuously conveyed through a diffusion trough, in passing through which it is sprayed with extraction liquid from liquor containers placed beneath the trough and in which it is subjected to preliminary water extraction by pressure means at the outlet end of the trough.

Extraction methods and apparatuses are known in which the bagasse is fed through a filling hopper and on to a stationary screen in the bottom of the diffusion trough the resulting layer of bagasse being carried forward at uniform speed through the trough by conveyor means, e.g., transverse bars attached at their ends to drag chains. To collect the spray liquid on passage through the screen, liquor containers are positioned side by side beneath the screen and extending over the entire length and width of the trough. The extraction liquid passing through the layer of bagasse can then be pumped out of the liquor containers with the aid of circulating pumps associated with each container and is returned to the bagasse layer upstream of the respective liquor container.

in this manner the extraction liquid penetrates through the bagasse layer cyclically from one liquor container to the next or from one spray distributor to the next, and becomes increasingly enriched with sugar in the direction of the bagasse inlet.

In order to apply pressure to the bagasse which has been subjected to extraction and is leaving the diffusion trough so as to obtain a moisture content enabling it to be burnt, a number of water extraction mills are disposed downstream of the outlet end of the trough, with which water extraction can be effected to the extent of about 50 percent prior to being burnt, and to reduce the number of water extraction mills following the diffusion trough, it has been proposed in the aforementioned U.S. Pat. No. 3,501,345 to effect a preliminary extraction of water from the bagasse at the end of the diffusion trough, prior to discharge at its outlet end. For this purpose the last part of the diffusion trough, i.e., the preliminary water extraction zone, contains one or more pressure rolls. These rolls can be driven and by suitable choice of gearing may have a peripheral speed which is periodically higher or lower than the rate of travel of the bagasse, so that a certain rearrangement of the layer of bagasse and internal friction in said layer are achieved. Rolls driven in this manner effect a preliminary extraction of water which tests have shown to amount to 25.1 percent after the first roll, 11.7 percent after the second, smaller roll, and 5.7 percent after the third, smallest roll.

Although, as compared with known extraction methods and devices preliminary extraction of water at the outlet end of the diffusion trough constitutes a considerable improvement, the capital cost and the cost of operating pressure rollers are relatively high.

Furthermore, the preliminary extraction of water effected by rolls is frequently not sufficient to enable one of the water extraction mills disposed downstream of the diffusion trough to be dispensed with in all cases. This disadvantage is all the more noticeable because the water extraction mills require considerable power and are subject to considerable wear, besides being costly.

This invention aims at eliminating the disadvantages of conventional methods and apparatuses and in particular improving the extraction of sugar and preliminary extraction of water at the end of the diffusion trough, while entailing relatively low capital expenditure and operating costs, so that even when only a single water extraction mill is disposed downstream of the diffusion trough, the residual moisture content of the bagasse enables it to be burnt.

This problem is solved according to this invention by operating the throughput of bagasse at uniform speed and causing a preliminary water extraction by subjecting the bagasse to the braking action of a single, undriven brake roll. The braking action of the roll, which results from the rolling resistance of the roll on the heavily compressed bagasse, which rolling resistance can be increased by the additional provision of a brake, and the consequent reduction of the rate of travel of the bagasse layer lead to the piling (damming) up of bagasse in front of the brake roll and to intensive rearrangement of the bagasse layer in the region of the roll.

In this manner it is possible with only a single undriven brake roller operating at a relatively low pressure, to obtain a reduction of the moisture content of the bagasse from 82 to 74 percent.

Particularly good results are obtained if in accordance with the invention the ratio of the diameter of the brake roller to the height of the layer of bagasse before entering the water extraction zone, i.e., in the region of the brake roll, amounts to from 1.5 to 3.121. It is desirable that the rate of travel of the bagasse in the extraction zone should be adjusted to the size of the brake roll.

According to the invention the rate of travel of the unbraked bagasse does not exceed, expressed in meters per minute, 30 percent of the diameter of the brake roll. If these values respected, a roll pressure of about 0.4 to 0.6 kg. per square cm. is sufiicient to secure preliminary water extraction in the diffusion trough to enable a water extraction mill to be dispensed with.

In order to achieve the greatest possible reduction of the residual sugar content at the end of the difiusion trough, pretreatment of the bagasse before it enters the diffuser has been found desirable. In order to enable the length of such diffusion troughs, which in any case amounts to 50 meters or more, to be limited for reasons of operation and cost, depths of the bagasse layer up to about 2 meters are used. For bacteriological reasons and in order to achieve plasmolysis of the crushed cane it is now necessary to spray the sugar cane for a short period with extraction liquid at a higher temperature after it has been crushed. At the same time the crushed cane is heated to the diffusion temperature required for the remainder of the process. According to the invention an amount of so-called circulating liquor which is increased by up to percent or more, is now necessary for the bacteriological pretreatment of the cane by elevated temperature treatment for a short period, in order to achieve the aim indicated.

With the customary layer depths of up to 2 meters, this increase in the amount of circulating liquor often gave rise to considerable difficulty because the increased volume of liquid could not penetrate a bed of this depth so that breakdowns in operation occurred.

According to a further feature of the invention the diffusion trough is preceded by a heating stage in which a spout capable of pivotal movements is disposed above a scraper conveyor and a baffle wall is disposed between the spout and the conveyor, initial mixing of circulating liquor and crushed cane taking place in the spout. Provision of the spout ensures distribution of the crushed cane over the scraper conveyor which works in the reverse direction. According to the invention the bagasse released from the spout strikes the baffle wall before entering the scraper conveyor. The reversal of the direction of movement between the spout and the scraper conveyor which is effected by this baffle wall results in intensive mixing, distribution, and uniform preheating of the bagasse by the increased amount of circulating liquor at higher temperature. In addition, the reverse direction of flow in the spout enables the overall length of the diffusion trough to be reduced.

In carrying out the method according to the invention, a roll provided with a brake device is disposed at the outlet end of the diffusion trough and at the inlet end, there are disposed a spout which pivots about a vertical axis, a scraper conveyor on to which material is discharged from the spout and by which it is moved in the opposite direction, and between the spout and conveyor a baffle plate is provided, so that the bagasse is brought into contact with an increased amount of circulating liquor at higher temperature.

Suitable control of the spout enables the layer of bagasse to be increased in depth on both sides of the trough, so that the excessively rapid percolation of the extraction liquid which is frequently observed in the region of or directly at the sidewalls of the diffusion trough is avoided.

Since the width of the brake roll is such that it extends from one wall of the trough to the other, there is a risk of pieces of sugar cane passing between the sidewalls of the diffusion trough and the end faces of the brake roll, which should it occur, might lead to stoppage of the plant.

To overcome this possibility, according to the invention the distance between the end plates of the brake roll is less than the width at the perimeter, so that end recesses are formed in which radially extending blades are disposed with the result that any pieces of sugar cane which enter are continuously dislodged upwardly and removed therefrom.

Another advantageous feature of the invention resides in the provision of return flow pipes from the liquor containers having a branch pipe or pipes each with a spray nozzle, the cross section of the first part of the pipe in the direction of flow being about three times as large as the cross section of the branch or other part of the pipe.

The effect is thereby achieved in contrast to known diffusion troughs in which only one liquor distributor is associated with each circulation pump, that 75 percent of the recirculating liquor is fed to the spray head which is first in the direction of flow while the remaining 25 percent of the extraction liquid from the respective container is supplied to the next following liquor spray or distributor, which is fed from the same liquor container.

Very unifonn distribution of the extraction liquid in the bagasse layer, and a correspondingly uniform wetting time for the particles of sugar cane, are thus achieved from one liquor distributor to the next in the direction of transport. The final effect is better extraction or reduction of the residual sugar content and therefore also a reduction in the length of the dif fusion trough.

The: method of the invention as applied to an apparatus operating on the countercurrent principle for extraction of bagasse, is illustrated in the accompanying drawings, in which:

FIG. I is a side elevation of a diffusion trough according to the invention,

FIG. 2 is an elevation on an enlarged scale ofthe inlet end of the diffusion trough of FIG. I,

FIG. 3 is a plan view, partly in section of the inlet end of the diffusion trough shown in FIG. 1,

FIG. 4 is a vertical section on the line lV-IV of FIG. 2, showing the inlet end ofthe diffusion trough.

FIG. 5 is a part view on an enlarged scale of the diffusion trough illustrated in FIG. 1,

FIG. 6 is an axial section ofa brake roll according to the invention, and

FIG. 7 an end view of the brake roll shown in FIG. 6.

The diffusion trough 11 consists of sidewall Ila, H12 and a screen forming the base 12, which extends upwardly at one end 13, while at the outlet end 14 it is open. Moveable over the upper side of the screen I2 is a conveyor belt consisting of drag chains 9 and transverse bars 10. Over the entire length and width of the diffusion trough II there are disposed beneath the screen 12 liquor containers I6 arranged side by side to receive the extraction liquid that percolates through the layer of bagasse. The extraction liquid that collects in the containers I6 is drawn off by means of circulating pumps 17 from each liquor container and is returned by branch pipes I8, at the ends of which are distributors or discharge nozzles 19. The nozzles 19 are distributed lengthwise of the extraction zone of the diffusion trough and each of them lies upstream of the liquor container I6 feeding it.

The conveyor 9-10 moves the bagasse at constant speed through the diffusion trough II, at the outlet end 14 of which All the bagasse is thrown by a throwing roll Ill on to a conveyor belt 221, which in turn discharges into the filling hopper of a conventional water extraction mill 23. In the preliminary water extraction zone of the diffusion trough I] an undriven brake roll 25 is mounted in a forked arm 24 capable of pivot ing about a horizontal axis.

The crushed sugar cane enters the trough via a conveyor belt 26 delivering into a filling hopper 27 disposed above a pivoted feed spout 28. In the swiveling spout 28 is a conveyor belt 29 which runs in a direction opposite to that of the bagasse in the diffusion trough Ill. The spout 28 swivels about a vertical axis 31, being supported at its free end by rollers 32 running on an arcuate guide rail 33 (FIG. 3).

Heated extraction liquid is fed to the bagasse in passage on the conveyor belt 29 from pipes 35 having discharge outlets above the conveyor 29.

Opposite the discharge end of the swiveling spout 28 is a baffle plate 36 which directs the bagasse leaving the conveyor belt 29 on to a scraper belt 37. Movement of the scraper belt 37 which consists essentially of a series of ribbed rolls 38 is opposite to the direction of movement of the conveyor belt 29. When the bagasse is transferred from the swiveling spout 28 to the scraper belt 37, the opposite directions of movement of the two conveyor belts results in an intensive rearrangement of the layer of bagasse, thus bringing about a rapid rise in the temperature of the latter through the hot extraction liquid from the spray pipes 35. Since the swiveling spout 28 is disposed above the scraper conveyor 37 and a rapid increase in temperature is brought about on the rearrangement of the bagasse, the diffusion trough 11 can be designed to have a relatively short overall length compared with conventional diffusion troughs. In addition, in consequence of the thorough mixing and intensive wetting, a particularly favorable increase of the Brix rating of about 1.5 is effected in the region of the swiveling spout 28 and scraper conveyor 37. At the same time the extraction liquid withdrawn from the liquor container 16 situated beneath the scraper conveyor .37 can again be fed to the bagasse in the region of the swiveling spout and/or of the scraper conveyor.

On discharge from the end of the scraper conveyor 37 the bagasse drops on to the screen 12, over which it is moved at a constant speed of travel to the outlet end 14 while being sprayed with extraction liquid.

The extraction liquid is fed to the bagasse by means of liquor distributors 19, each two adjacent distributors being fed from a single liquor container l6 or by means ofa single circulating pump I7 (FIG. 5). For this purpose the supply pipes 18 of the circulating pumps 17 have two branch pipes and [8b. The cross section of pipe 180 is three times as great as that of the pipe 18b, so that 75 percent of the liquid flow 18 can be fed through the pipe 18a or the respective liquor distributor to the bagasse, while 25 percent passes out through the pipe I8! and its distributor. Very uniform distribution of liquid in the direction of transport is thereby achieved.

In the water extraction zone, which is characterized by the brake roll 25 and the absence of liquor distributors 19, in the diffusion trough II, the bagasse layer undergoes compression by the brake roll at a pressure of about 0.4 to 0.6 kg. per square cm., and water is thereby extracted. Brake roll 25 is under control ofa brake device (FIG. 6) in such a manner that its peripheral speed is lower than the speed of travel of the bagasse in the extraction zone of the diffusion trough. The consequent lower speed of the bagasse in the preliminary water extraction zone leads to the piling (damming) up of the bagasse in front of the brake roll 25 and thus to an increase in the duration of squeezing and at the same time to an intensive rearrangement of the layer of bagasse and internal friction in the latter in the region of the roll. This leads to a reduction of the moisture content of the bagasse in the preliminary water extraction zone of the diffusion trough 11 from about 82 to 74 percent.

The brake roll 25 has a peripheral wall M and end plates 42 and 43, through which a horizontal shaft $4 extends. On the shaft 44 there is fast a brake wheel 39 to which a braking action can be applied by a lever 40. The end faces 42, 43 are inset in relation to the peripheral wall 41, so that end recesses 45, 46 are formed. Radial blades 47 and/or a cone ring 470 fastened on the end faces 42, 43 are situated in these end chambers by which any particle of sugar cane entering the gap between the brake roll 25 and the trough walls 11a and 11b is removed,

The ratio of the diameter of the brake roll 25 to the depth of the layer of bagasse in the extraction zone is from 1.5 to 3.0: 1, while the rate of travel of the bagasse in the extraction zone amounts to 30 percent of the roll diameter, expressed in meters per minute, and the pressure exerted by the brake roll is from 0.4 to 0.6 kg. per square cm. Experiments carried out on this basis have shown that the desired preliminary extraction of water, that is to say the reduction of the moisture content of the bagasse from 82 to 74 percent is accompanied by only a very slight increase in power input. Measurements have in fact shown that an increase of the pressure by 43 percent resulted in a rise in power input from 4.14 to only 4.25 amps. On the other hand, in a comparative test in which the above-mentioned specific values were not respected, the power input rose to 67 amps. An increase of the power input of this type can be overcome only if at the same time the gearing working with very high transmissions ratios are strengthened accordingly. The invention, however, makes such a strengthening unnecessary.

What is claimed is:

1. ln apparatus for the continuous extraction of sugar from bagasse or comminuted sugar cane, the combination of a diffusion trough having a perforated bottom for the bagasse conveyor means for conveying the bagasse from the inlet to the discharge end of the trough; spray means for subjecting the layer of bagasse in passage over the screen to the action of extraction liquid; container means located beneath the perforated bottom for collection of extraction liquor; means for recirculation of liquor to the spray means; means including a feed spout through which bagasse is fed on to the screen at the inlet end of the trough, said spout being supported for traversing movements relative to the trough; freely rotatable roll positioned at the discharge end of the trough for maintaining pressure on the layer of bagasse and a braking device for controlling the rate of rotation of the roll and thus the output from the diffusion trough.

2. The combination according to claim 1 in which beneath the feed spout there is disposed delivery means including a scraper conveyor. on to one end of which conveyor the spout discharges, the direction of travel of which conveyor is opposite to the direction of delivery of material from the spout.

3. Apparatus according to claim 2 in which a baffle plate is disposed between the feed spout and the scraper conveyor.

4. ln apparatus for the continuous extraction of sugar from bagasse or comminuted sugar cane, the combination of a diffusion trough having a perforated bottom for the bagasse; conveyor means for conveying the bagasse from the inlet to the discharge end of the trough; spray means for subjecting the layer of bagasse in passage over the perforated bottom to the action of extraction liquid; container means located beneath the perforated bottom for collection of extraction liquor; means for recirculation of liquor to the spray means; means including a feed spout through which bagasse is fed on to the perforated bottom at the inlet end of the trough, said spout being supported for traversing movements relative to the trough; a roll positioned at the discharge end of the trough for maintaining pressure on the layer of bagasse and a braking device for controlling the rate of rotation of the roll and thus the output from the diffusion trough, a roller frame, a roll joumaled to revolve freely in the frame, said roll having an axial recess at each end and scraper blades carried by the roller frame and extending into the recesses to remove material accumulating in the recesses.

5. ln apparatus for the continuous extraction of sugar from bagasse or comminuted su ar cane, the combination of a diffusion trough having a pe orated bottom for the bagasse; conveyor means for conveying the bagasse from the inlet to the discharge end of the trough; spray means for subjecting the layer of bagasse in passage over the perforated bottom to the action of extraction liquid; container means located beneath the perforated bottom for collection of extraction liquor; means for recirculation of liquor to the spray means; means including a feed spout through which bagasse is fed on to the perforated bottom at the inlet end of the trough, said spout being supported for traversing movements relative to the trough; a roll positioned at the discharge end of the trough for maintaining pressure on the layer of bagasse and a braking device for controlling the rate of rotation of the roll and thus the output from the diffusion trough, said means for recirculation of extraction liquor comprising circulating pumps associated with each liquor container, return flow pipes connecting said pumps to the spray means, each return pipe including first and second pipe portions, the pipe portion which is first in the direction of flow of the bagasse being not less than substantially three times as large as the cross section of the second pipe portion. 

2. The combination according to claim 1 in which beneath the feed spout there is disposed delivery means including a scraper conveyor. on to one end of which conveyor the spout discharges, the direction of travel of which conveyor is opposite to the direction of delivery of material from the spout.
 3. Apparatus according to claim 2 in which a baffle plate is disposed between the feed spout and the scraper conveyor.
 4. In apparatus for the continuous extraction of sugar from bagasse or comminuted sugar cane, the combination of a diffusion trough having a perforated bottom for the bagasse; conveyor means for conveying the bagasse from the inlet to the discharge end of the trough; spray means for subjecting the layer of bagasse in passage over the perforated bottom to the action of extraction liquid; container means located beneath the perforated bottom for collection of extraction liquor; means for recirculation of liquor to the spray means; means including a feed spout through which bagasse is fed on to the perforated bottom at the inlet end of the trough, said spout being supported for traversing movements relative to the trough; a roll positioned at the discharge end of the trough for maintaining pressure on the layer of bagasse and a braking device for controlling the rate of rotation of the roll and thus the output from the diffusion trough, a roller frame, a roll journaled to revolve freely in the frame, said roll having an axial recess at each end and scraper blades carried by the roller frame and extending into the recesses to remove material accumulating in the recesses.
 5. In apparatus for the continuous extraction of sugar from bagasse or comminuted sugar cane, the combination of a diffusion trough having a perforated bottom for the bagasse; conveyor means for conveying the bagasse from the inlet to the discharge end of the trough; spray means for subjecting the layer of bagasse in passage over the perforated bottom to the action of extraction liquid; container means located beneath the perforated bottom for collection of extraction liquor; means for recirculation of liquor to the spray means; means including a feed spout through which bagasse is fed on to the perforated bottom at the inlet end of the trough, said spout being supported for traversing movements relative to the trough; a roll positioned at the discharge end of the trough for maintaining pressure on the layer of Bagasse and a braking device for controlling the rate of rotation of the roll and thus the output from the diffusion trough, said means for recirculation of extraction liquor comprising circulating pumps associated with each liquor container, return flow pipes connecting said pumps to the spray means, each return pipe including first and second pipe portions, the pipe portion which is first in the direction of flow of the bagasse being not less than substantially three times as large as the cross section of the second pipe portion. 